Implantable neuromodulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations, Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Furthermore, Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
These implantable neuromodulation systems typically include one or more electrode carrying modulation leads, which are implanted at the desired stimulation site, and a neuromodulator (e.g., an implantable pulse generator (IPG)) implanted remotely from the stimulation site, but coupled either directly to the modulation lead(s) or indirectly to the modulation lead(s) via a lead extension. The neuromodulation system may further comprise an external control device to remotely instruct the neuromodulator to generate electrical modulation pulses in accordance with selected modulation parameters.
Electrical modulation energy may be delivered from the neuromodulator to the electrodes in the form of a pulsed electrical waveform. Thus, modulation energy may be controllably delivered to the electrodes to stimulate neural tissue. The combination of electrodes used to deliver electrical pulses to the targeted tissue constitutes an electrode combination, with the electrodes capable of being selectively programmed to act as anodes (positive), cathodes (negative), or left off (zero). In other words, an electrode combination represents the polarity being positive, negative, or zero. Other parameters that may be controlled or varied include the amplitude, duration, and rate of the electrical pulses provided through the electrode array. Each electrode combination, along with the electrical pulse parameters, can be referred to as a “modulation parameter set.”
With some neuromodulation systems, and in particular, those with independently controlled current or voltage sources, the distribution of the current to the electrodes (including the case of the neuromodulator, which may act as an electrode) may be varied such that the current is supplied via numerous different electrode configurations. In different configurations, the electrodes may provide current or voltage in different relative percentages of positive and negative current or voltage to create different electrical current distributions (i.e., fractionalized electrode configurations).
As briefly discussed above, an external control device can be used to instruct the neuromodulator to generate electrical modulation pulses in accordance with the selected modulation parameters. Typically, the modulation parameters programmed into the neuromodulator can be adjusted by manipulating controls on the external control device to modify the electrical stimulation provided by the neuromodulator system to the patient. However, the number of electrodes available combined with the ability to generate a variety of complex modulation pulses, presents a vast selection of modulation parameter sets to the clinician or patient.
To facilitate such selection, the clinician generally programs the neuromodulator through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC). The PC or custom hardware may actively control the characteristics of the electrical stimulation generated by the neuromodulator to allow the optimum modulation parameters to be determined based on patient feedback or other means and to subsequently program the neuromodulator with the optimum modulation parameter set or sets, which will typically be those that stimulate all of the target tissue in order to provide the therapeutic benefit, yet minimizes the volume of non-target tissue that is stimulated. The computerized programming system may be operated by a clinician attending the patient in several scenarios.
Often, multiple timing channels are used when applying electrical modulation energy to target different tissue regions in a patient. For example, in the context of SCS, the patient may simultaneously experience pain in different regions (such as the lower back, left arm, and right leg) that would require the electrical stimulation of different spinal cord tissue regions. In the context of DBS, a multitude of brain structures may need to be electrically stimulated in order to simultaneously treat ailments associated with these brain structures. Each timing channel identifies the combination of electrodes used to deliver electrical pulses to the targeted tissue, as well as the characteristics of the current (pulse amplitude, pulse duration, pulse rate, etc.) flowing through the electrodes.
As is conventional, the ability of each timing channel to generate modulation energy it typically limited. For example, the maximum pulse amplitude and/or pulse rate that each timing channel can provide may be limited. Furthermore, the nature of the pulse rate for each timing channel may be limited in that it must be uniform. Although these timing channels can be used in combination for providing modulation energy to different tissue regions of a patient, most often, there are restrictions on operating the timing channels together (e.g., the maximum rate of each channel may be limited when multiple timing channels are programmed to operate simultaneously). Furthermore, the timing channels are often operated independent of each other to create separate modulation effects that the different tissue regions. While neuromodulation systems can be designed with hardware capable of addressing these concerns, redesigning the hardware on presently existing neuromodulation designs to accommodate these pulse trains may be a monumental task. Furthermore, neuromodulation systems that are currently used in the field may not be easily updated to eliminate these limitations from the timing channels.
There, thus, remains a need to provide an improved technique for increasing the modulation flexibility of presently existing multi-channel neuromodulation systems.